GB2293637A

GB2293637A - Clutch control system with anti-vibration slip control and automatic wear adjustment

Info

Publication number: GB2293637A
Application number: GB9519896A
Authority: GB
Inventors: Jurgen Kleifges; Jorg Sudau; Bernhard Schierling; Thomas Wirth; Michael Weiss
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1994-09-29
Filing date: 1995-09-29
Publication date: 1996-04-03
Anticipated expiration: 2015-09-29
Also published as: DE4434762B4; GB2293637B; DE4434762A1; GB9519896D0; FR2725255B1; FR2725255A1

Description

1 FRICTION CLUTCH 2293637 The invention relates to a friction clutch of

the kind used with a motor vehicle internal combustion engine for transmitting torque from the engine crankshaft to a gearbox shaft, and comprising a flywheel connected to the crankshaft, a rotatable pressure plate means including a clutch housing and a pressure plate rotatable with the clutch housing but movable axially relative thereto, an actuating means urging the pressure plate towards the flywheel, a clutch plate with friction linings for engagement between the pressure plate and the flywheel, the clutch plate being carried by a hub mounted for rotation with the gearbox shaft, and a clutch actuating system.

DE 41 00 372 shows the provision of slip control in a friction clutch of the kind set forth when torsional vibrations occur in the drive train. The torsional vibrations can at least be reduced to a harmless level by the use of a deliberate amount of slip between the clutch plate and the flywheel, but this may increase the wear on the friction linings.

DE 29 20 932 shows a friction clutch of the kind set forth with an automatic wear compensation device, whereby the travel relationships of the withdrawal system are maintained substantially constant and the actuating force provided by the actuating means is substantially unchanged throughout the life of the clutch.

It is an aim of the present invention, in a friction clutch of the kind set forth, to reduce torsional vibrations in the drive train by slip modulation and simultaneously to ensure that the clutch has a long working life without an expensive construction.

2 According to the present invention, in a friction clutch of the kind set forth the pressure plate means includes an automatic wear adjuster operative to maintain a substantially constant rest position of the clutch actuating system relative to the flywheel, independent of the thickness of the friction linings, the actuating system is operated by electronic control means which produces slip between the clutch plate and the flywheel when torsional vibrations occur in the drive train, and each friction lining has a wear reserve of between about 1.5mm and 4mm.

This combination of features makes it possible, despite slip modulation and the associated increased wear of the friction linings (the amount of slip can be large for natural frequency vibrations in the drive train), to maintain a constant operational behaviour of the clutch over a long period of time. The automatic wear adjuster ensures that the basic requirement for clutch actuation, by a withdrawal system part of the actuating system, is kept substantially constant, as is the actuating force produced by the actuating means of the clutch. The combination of the wear adjuster with a larger wear reserve in the form of thicker friction linings, achieves a long working life for the clutch.

Preferably, the actuating means comprises a spring. The spring preferably comprises a diaphragm spring provided with radially inwardly projecting spring tongues for engagement by a withdrawal system of the actuating system. Such a spring both produces the spring force and acts as a withdrawal lever, so providing a particularly economical construction.

Advantageously the clutch plate includes a torsional vibration damper with a friction device having a very low friction force. The low friction force is preferably less than about 3 Nm. With such a low 3 friction force the torsional vibrations in the drive train have increased peak values in the range of the natural frequencies, but the speed range within which such vibrations arise is reduced. This ensures that a minimum slip modulation is required in operation.

Preferably the flywheel comprises a two-mass flywheel with a torsional vibration damper arranged between the two relatively rotatable masses. This damper is advantageously so tuned that its friction device has a very low friction force.

In a particularly advantageous manner the ratio of the outside diameter to the inside diameter of the friction linings is less than 1.4. It has been found that in a clutch plate with such a diameter ratio, a very high specific surface loading can be provided without difficulty, thereby improving the engagement of the friction linings against the opposing friction surfaces with a minimum thermal distortion, whereby local thermal overloads can be greatly reduced. This diameter ratio also provides a low moment of inertia of the clutch plate, so that for example the gear-changing behaviour in the gearbox can be improved.

An embodiment of the invention is illustrated by way of example in the accompanying drawing, which shows a longitudinal section through a friction clutch.

The friction clutch 1 shown is for transmitting torque from an engine crankshaft to a gearbox shaft 11 of a motor vehicle. The clutch has a flywheel 2 connected to the crankshaft of an internal combustion engine (not shown). The flywheel 2 and crankshaft define a common axis of rotation 5. A rotatable pressure plate means is secured on the flywheel 2, and includes a clutch housing 3, and a pressure plate 4 arranged in the 4 clutch housing 3. The pressure plate 4 is mounted to rotate with the housing 3 but to be axially displaceable relative thereto. This is achieved by means of tangential leaf springs (not shown). An actuating means comprising a diaphragm spring 6 is located between the pressure plate 4 and the clutch housing 3. The diaphragm spring 6 abuts at an intermediate diameter against the clutch housing 3 and acts at its outside diameter on the pressure plate 4. The spring 6 also has radially inwardly projecting spring tongues 7, formed in such a way that they can be acted on by a withdrawal thrust bearing 12. The withdrawal bearing 12 is 10 connected through a withdrawal fork lever 13 to an electronic control is means 14 which is provided with a number of sensor inputs 15. Information from the inputs 15 is used by the control means 14 to control the actuation of the clutch. The control means 14 and withdrawal system 12, 13 form clutch actuating means. Between the pressure plate 4 and the flywheel 2 there is a clutch plate 8. The clutch plate 8 is carried by a hub 10 which is mounted on the gearbox shaft 11 to rotate with it. The clutch plate 8 has friction linings 9 in its radially outer region, these linings being adapted to be frictionally engaged by the pressure plate 4 and the flywheel 2. The clutch plate 8 also has a torsional vibration damper 20 arranged to operate between the friction linings 9 and the hub 10.

An automatic wear adjuster 16 is provided between the radially outer region of the diaphragm spring 6 and the pressure plate 4. The adjuster 16 includes a rotatable ring 18 which has inclined faces cooperating with corresponding opposed inclined faces on the pressure plate 4, to alter the axial spacing between the pressure plate 4 and the diaphragm spring 6. An adjustable travel-limiting device 17 is also provided. Spring means comprising several circumferentially spaced springs 19 apply a torque to the rotatable ring 18. The ratio of the outside diameter Da to the inside diameter Di of the friction linings 9 has a value of less than 1.4. The friction linings 9 are of such a thickness that each of the linings has a wear reserve of between about 1.5 mm and 4 MM.

In operation actuation of the clutch 1 takes place through the electronic control means 14 which operates through appropriate sensor inputs 15 in order to actuate the clutch in the desired manner. For example the control means 14 may receive information from the sensor inputs on the position of the accelerator pedal, and the rotational speeds of the engine and the gearbox shaft 11. When the electronic control means 14 detects torsional vibrations in the drive train, it causes partial disengagement of the clutch 1 through the withdrawal fork 13 and the thrust bearing 12. The introduces a degree of slip between the friction linings 9 on the clutch plate 8 and the flywheel 2 and pressure plate 4.

This type of operation means that the friction linings 9 are subjected to increased wear. In order to cope with this increased wear, the friction linings 9 are thicker, and the automatic adjuster 16 is operative. On increased wear the adjustable travel-limiting device 17 will limit the withdrawal movement of the pressure plate 4 before the withdrawal sequence of the clutch 1 is completed, so that the radially outer region of the diaphragm spring 6 lifts away from the rotatable ring 18 by a distance equal to the wear which has occurred and the springs 19 then operate to move the ring 18 sufficiently far so that the effect of the inclined surfaces is to take up the gap between the ring 18 and diaphragm spring 6. The adjuster 16 thus ensures that the diaphragm spring 6 is held substantially in the position in which it was installed so that the load exerted by it on the pressure plate 4 remains constant. The position of the withdrawal thrust bearing 12 relative to the fork 13 remains unchanged so that at this point there is no increase in the axial space taken up and the actuation of the clutch through the control means 14 is unaffected. The torsional 6 vibration damper 20 is arranged so that its friction devices exert a very small friction force (less than about 3Nm). This has the result that for torsional vibrations within the natural frequency range, the speed range of these vibrations is greatly reduced so that de-coupling of the vibrations by the use of slip is necessary for only a relatively brief period as this speed range is passed through. The wear of the friction linings 9 is therefore reduced to a minimum. Furthermore, the ratio of the outside diameter Da to the inside diameter Di of the friction linings 9 of less than 1.4 is suited to allow very low-wear operation over a long time period. With such a 10 ratio, the friction linings 9 are relatively narrow in a radial direction. They therefore allow a high specific loading as the heat generated during slip results in only a small thermal distortion of the linings 9 and the local overloads within the friction surfaces are greatly reduced.

is In a modification, not shown, the flywheel 2 may be a two-mass flywheel, having two relatively rotatable masses with a torsional vibration damper arranged between them. As with the torsional vibration damper 20, a damper in the flywheel is arranged so that its friction devices exert a very small friction force.

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Claims

1. A friction clutch of the kind set forth, in which the pressure plate means includes an automatic wear adjuster operative to maintain a substantially constant rest position of the clutch actuating system relative to the flywheel independent of the thickness of the friction linings, the actuating system is operated by electronic control means which produces slip between the clutch plate and the flywheel when torsional vibrations occur in the drive train, and each friction lining has a wear reserve of 10 between about 1.5mm and 4mm.

2. A friction clutch as claimed in claim 1, in which the actuating means comprises a spring.

3. A friction clutch as claimed in claim 2, in which the spring comprises a diaphragm spring provided with radially inwardly projecting spring tongues for engagement by a withdrawal system of the actuating system.

4. A friction clutch as claimed in any preceding claim, in which the clutch plate includes a torsional vibration damper with a friction device having a very low friction force.

5. A friction clutch as claimed in claim 4, in which the friction force 25 is less than about 3Nm.

6. A friction clutch as claimed in any preceding claim, in which the flywheel comprises a two-mass flywheel with a torsional vibration damper arranged between two relatively rotatable masses.

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7. A friction clutch as claimed in claim 6, in which the friction device of the torsional vibration damper has a very low friction force.

8. A friction clutch as claimed in any preceding claim, in which the ratio of the outside diameter to the inside diameter of the friction linings is less than 1.4.

9. A friction clutch of the kind set forth substantially as described herein with reference to and as illustrated in the accompanying drawing.